We just wrote an full-featured ruby library to scrape listings. Too we packaged it with a useful script to automate daily email reports on new posts. Everything’s well documented, and we hope it takes off as the de-facto ruby-craigslist library: Check it out in action here: http://www.derosetechnologies.com/community/libcraigscrape

Try CraigSpy - it lets you search multiple keywords (including AND/NOT keyword features,) multiple locations, multiple categories, and it also automatically searches for you while you’re away from the computer. http://www.craig-spy.com is the site